Seperating years on a plot

Hi 

I have been using Power BI for a month or so now, but one thing I cannot get my head around is how to plit up a time based graph to show a different line for each year and overlay them.

I have an old historic data set which cover 2015, 2016 and 2017 in a single data table and my new data which is pulled in from sharepoint.  

But the old data Only plots as one line, whereas I would like a line for each year.

I would love it to look more like this

Pleae help - i'm getting desperate!

Thanks

Chris